Apparatus and method for performing hybrid automatic repeat request operation in wireless communication system supporting carrier aggregation

ABSTRACT

Provided is a method of performing HARQ by a UE in a wireless communication system that supports carrier aggregation (CA). The method includes: receiving, from an evolved nodeB (eNB), a downlink grant on a first Physical Downlink Control Channel (PDCCH), the downlink grant including an accumulated downlink assignment indicator (A-DAI) field and a total DAI (T-DAI) field; receiving a first PDSCH indicated by the first PDCCH, the first PDSCH being transmitted from the eNB; receiving, from the eNB, an uplink grant on a second PDCCH, the uplink grant indicating a transmission of a Physical Uplink Shared Channel (PUSCH); determining a size of a HARQ-ACK codebook to which a HARQ-ACK with respect to the first PDSCH is to be mapped, based on the A-DAI and the T-DAI; and transmitting, to the eNB, the HARQ-ACK with respect to the first PDSCH on the PUSCH.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2015-0156038, filed on Nov. 6, 2015, which is herebyincorporated by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates to wireless communication that supportscarrier aggregation, and more particularly, to a method and apparatusfor determining the size of a HARQ-ACK codebook on an uplink datatransmission channel and for executing a HARQ operation based on aHARQ-ACK codebook of the determined size.

2. Discussion of the Background

Carrier aggregation (CA) is referred to as spectrum aggregation orbandwidth aggregation, which supports a plurality of carriers. Anindividual unit frequency bound by CA is referred to as a serving cellor a component carrier (CC). Each serving cell is defined by a bandwidthand a center frequency. CA provides the same effect as the case in whicha plurality of bands, which are physically continuous or non-continuousin the frequency domain, are bound and used as a logically large band.

As wireless communication traffic rapidly increases, the introduction ofa licensed assisted access (LAA) has been considered. This is a schemeof performing CA by utilizing frequencies of an unlicensed band inaddition to a licensed band that is exclusively allocated to a mobilecarrier. Using LAA, a UE may utilize a larger number of serving cells (amaximum of 32 serving cells) than the number of serving cells that maybe aggregable in an existing licensed band.

When an increased number of serving cells are configured by CA for a UE,the number of downlink data channels increases based on the number ofserving cells. Accordingly, a larger number of HARQ ACKs, which indicatewhether a downlink data channel is successfully received, need to betransmitted from the UE to an eNB. Here, the HARQ ACK may be transmittedon a new uplink control channel (PUCCH format 4 or 5), or may betransmitted together with an uplink data channel (which is referred toas piggyback). When an ACK or a NACK associated with a plurality ofdownlink data channels is transmitted on a single associated uplink datachannel, a combination of an ACK or a NACK with respect to each downlinkdata channel may correspond to a single code included in a HARQ ACKcodebook. Therefore, a UE determines an ACK or a NACK with respect to adownlink data channel that the UE receives, and then generates aHARQ-ACK based on a HARQ ACK codebook.

In the case of LAA, a channel associated with an unlicensed band israndomly obtained, and thus, the number of downlink data channelsdynamically changes. Accordingly, the size of a HARQ ACK codebook thatpiggybacks on an uplink data channel also dynamically changes. In thisinstance, the UE transmits a HARQ ACK based on a HARQ ACK codebook witha size that is determined based on downlink data channels that the UErecognizes. When the UE fails to recognize some downlink data channelsdue to the deterioration of a channel condition, the size of the HARQACK codebook that the UE makes reference to and the size of the HARQ ACKcodebook that the eNB actually intends to determine may be differentfrom each other.

Therefore, to enable the UE to successfully encode a HARQ ACK and toenable the eNB to successfully decode the HARQ ACK, both the UE and theeNB are required to accurately recognize the size of a HARQ ACK codebookthat dynamically changes. However, a technology that enables the abovehas not yet been disclosed and thus, there is a desire to overcome thedrawback thereof.

SUMMARY

Both a UE and an eNB are capable of accurately recognizing the size of aHARQ ACK codebook that dynamically changes. Also, an uplink HARQ-ACKoverhead may be effectively controlled and the reliable uplinktransmission and downlink data performance may be secured.

Particularly, the eNB sets the size of a HARQ ACK codebook thatdynamically changes by taking into consideration configured servingcell(s). In other words, through a scheme that sets the size of a HARQACK codebook based on an A-DAI value and a T-DAI value and thatindicates the same to the UE through a piece of control information, asystem supports the UE in effectively performing a HARQ operation. Asthe size of a HARQ ACK codebook is dynamically determined with respectto serving cell(s) configured by the UE, and because an overhead withrespect to an uplink HARQ ACK transmission is efficiently configured bytaking into consideration the determined size of the HARQ ACK codebook,HARQ with respect to actually scheduled data transmission may becontrolled Also, a scheme may efficiently generate a HARQ ACK codebookif it determines the size of a HARQ ACK codebook by taking into accountthe association relationship between an SPS PDSCH transmission and aMIMO transmission mode through which 2TBs are transmitted. Accordingly,the UE and the eNB may efficiently perform data transmission/reception.

According to an exemplary embodiment, there is provided a method ofperforming hybrid automatic repeat request (HARQ) by a user equipment(UE) in a wireless communication system that supports carrieraggregation (CA), the method including: receiving, from an evolved nodeB(eNB), a downlink grant on a first Physical Downlink Control Channel(PDCCH), the downlink grant including an accumulated downlink assignmentindicator (A-DAI) field and a total DAI (T-DAI) field, the A-DAI fieldindicating a sum of the number of PDCCHs indicating semi persistentscheduling (SPS) release and the number of Physical Downlink SharedChannels (PDSCHs) accumulated up to a current subframe within a bundlingwindow associated with HARQ-ACK reporting of the UE based on at leastone serving cell, and the T-DAI field indicating a sum of the number ofPDCCHs indicating SPS release and the number of all PDSCHs scheduled inassociation with HARQ-ACK reporting of the UE; receiving a first PDSCHindicated by the first PDCCH, the first PDSCH being transmitted from theeNB; receiving, from the eNB, an uplink grant on a second PDCCH, theuplink grant indicating a transmission of a Physical Uplink SharedChannel (PUSCH); determining a size of a HARQ-ACK codebook to which aHARQ-ACK with respect to the first PDSCH is to be mapped, based on theA-DAI and the T-DAI; and transmitting, to the eNB, the HARQ-ACK withrespect to the first PDSCH on the PUSCH.

According to an exemplary embodiment, there is provided a user equipment(UE) to perform hybrid automatic repeat request (HARQ) in a wirelesscommunication system that supports carrier aggregation (CA), the UEincluding: an RF circuit that receives, from an evolved node B (eNB), adownlink grant on a first Physical Downlink Control Channel (PDCCH),receives a first PDSCH indicated by the first PDCCH, the first PDSCHbeing transmitted from the eNB, and receives, from the eNB, an uplinkgrant on a second PDCCH, the uplink grant indicating a transmission of aPhysical Uplink Shared Channel (PUSCH), wherein the downlink grantincludes an accumulated downlink assignment indicator (A-DAI) field anda total DAI (T-DAI) field, the A-DAI field indicates a sum of the numberof PDCCHs indicating semi persistent scheduling (SPS) release and thenumber of Physical Downlink Shared Channels (PDSCHs) accumulated up to acurrent subframe within a bundling window associated with HARQ-ACKreporting of the UE based on at least one serving cell, and the T-DAIfield indicates a sum of the number of PDCCHs indicating SPS release andthe number of all PDSCHs scheduled in association with HARQ-ACKreporting of the UE; and a processor that determines a size of aHARQ-ACK codebook to which a HARQ-ACK with respect to the first PDSCH isto be mapped, based on the A-DAI and the T-DAI, and generates a HARQ-ACKwith respect to the first PDSCH. The RF circuit transmits, to the eNB,the HARQ-ACK with respect to the first PDSCH on the PUSCH.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are diagrams illustrating an example of applying adownlink grant including an A-DAI field and a T-DAI field to an FDD orTDD PUCCH cell group according to the present disclosure.

FIG. 2 is a diagram illustrating a method of calculating the size of aHARQ-ACK codebook according to a second embodiment of the presentdisclosure.

FIG. 3 is a diagram illustrating a method of determining the size of aHARQ-ACK codebook when a DL SPS PDSCH transmission exists according toan example of the present disclosure.

FIG. 4 is a diagram illustrating a method of determining the size of aHARQ-ACK codebook when a DL SPS PDSCH transmission exists according toanother example of the present disclosure.

FIG. 5 is a flowchart illustrating a method for a UE to transmit aHARQ-ACK according to an example of the present disclosure.

FIG. 6 is a flowchart illustrating a method for a UE to transmit aHARQ-ACK according to another example of the present disclosure.

FIG. 7 is a flowchart illustrating a method for an eNB to receive aHARQ-ACK according to an example of the present disclosure.

FIG. 8 is a flowchart illustrating a method for an eNB to receive aHARQ-ACK according to another example of the present disclosure.

FIG. 9 is a block diagram illustrating a UE and an eNB according to anexample of the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, license assisted access (LAA) refers to a wirelesscommunication scheme that supports a CA operation with respect to one ormore secondary serving cells (SCells) that operate in an unlicensed bandor an unlicensed spectrum, based on the assistance of a primary servingcell (PCell) that operates in a licensed band or a licensed spectrum. Inother words, LAA refers to a scheme that binds a licensed band and anunlicensed band through CA by using a carrier in an LTE licensed band(licensed carrier (LC)) as an anchor. A UE may access a network througha licensed band and use a service, and an eNB aggregates a licensed bandand an unlicensed band through CA and offloads traffic from the licensedband into the unlicensed band, depending on the situation.

A communication system that is capable of configuring serving cells fora UE through CA from at least five serving cells to a maximum of 32serving cells may be capable of controlling the size of a HARQ-ACKcodebook dynamically or of being adaptive to a channel condition, inaddition to determining the size of a HARQ-ACK codebook semi-statically,a function which is led by a higher layer such as RRC. The schemeenables an effective control of an uplink HARQ-ACK overhead and itsecures a reliable uplink transmission and downlink data performance.

Therefore, when a maximum of 32 serving cells are configured for a UE,the operations of a higher layer, such as RRC may include at least oneout of operations (1) to (4) provided below.

(1) HARQ-ACK Codebook Configuration

The operation of a higher layer may include an indication operationwhich is associated with whether a semi-static HARQ-ACK codebookconfiguration or a dynamic HARQ-ACK codebook configuration is to beapplied. To this end, an eNB may transmit, to a UE, informationindicating the configuration of a semi-static HARQ-ACK codebook or adynamic HARQ-ACK codebook. The semi-static HARQ-ACK codebookconfiguration is a first mode in which the eNB transmits, to the UE, ahigher layer signaling associated with the size of a HARQ-ACK codebook.The dynamic HARQ-ACK codebook configuration is a second mode in whichthe eNB transmits, to the UE, a higher layer signaling associated withthe size of a HARQ-ACK codebook. In the second mode, the UE needs todetermine (predict, or decide) the size of a dynamic HARQ-ACK codebookbased on information that is different from a higher layer signaling,which will be described later through detailed embodiments.

The reason that the modes are distinguished as described above is that ascheme of applying a dynamic HARQ-ACK codebook may increase thecomplexity of the embodiment of an eNB and a UE when compared to a gainassociated with the purpose of optimizing the size of a HARQ-ACKcodebook when the number of serving cells is about 6 to 7. Therefore, inthe case of CA of 5 or more serving cells, the configuration of aHARQ-ACK codebook size based on semi-static parameters needs to besupported.

(2) FDD/TDD PUCCH Cell Group Configuration

The operation of a higher layer may include an FDD/TDD PUCCH cell groupconfiguration. For example, when a PUCCH SCell is not configured, only asingle cell group including a PCell may exist. In this instance, theconcept of a cell group is not applied, and thus, the environment isidentical to the existing environment. As another example, when a PUCCHSCell is configured, a maximum of two PUCCH cell groups may beconfigured.

(3) Serving Cell Configuration Including More than 5 Serving Cells inFDD CA or TDD CA (Including TDD-FDD CA)

The operation of a higher layer may include configuring more than 5serving cells in FDD CA or TDD CA (including TDD-FDD CA). In TDD CA orTDD-FDD CA, a plurality of downlink subframes may be associated with asingle uplink subframe as a bundling window. In this instance, although5 or fewer serving cells are configured, a larger number of HARQ-ACKbits may be generated (e.g., the number of HARQ-ACK bits >22).Therefore, in TDD CA or TDD-FDD CA, the number of serving cells may bedetermined based on 22 bits, which is the maximum HARQ-ACK bit size thatPUCCH format 3 may transmit.

(4) PUCCH Format 4 or 5 Configuration

The operation of a higher layer may include setting an RRC parameterrequired for the configuration of PUCCH format 4 or 5.

When the dynamic HARQ-ACK codebook configuration (second mode) isapplied to a UE and/or an eNB, the UE may determine (predict or decide)the size of a HARQ-ACK codebook based on downlink control information(DCI).

The DCI is information that is transmitted by being mapped onto a PDCCHor an EPDCCH, and includes a downlink grant that schedules a downlinkdata transmission and an uplink grant that schedules an uplink datatransmission. According to the present embodiment, when a maximum of 32serving cells are configured for a UE, DCI may include at least one outof an accumulated downlink assignment indicator (A-DAI) field and atotal downlink assignment indicator (T-DAI) field. Alternatively, theDCI may include a single integrated DAI field that includes an indicatorconveyed by both the A-DAI and the T-DAI. In the following embodiments,although the descriptions are provided by assuming the case in which theindication conveyed by the T-DAI is provided through a separate T-DAIfield, the indication and a processing method thereof are equallyapplied even in the case of an integrated DAI field.

The A-DAI is included in a downlink grant (DL A-DAI). A UL DAI exists inan uplink grant.

The DL A-DAI indicates the number of downlink (E)PDCCHs indicating SPSrelease and the number of PDSCHs accumulated up to a current subframe ina bundling window/serving cell CC set based on at least one servingcell. The DL A-DAI is transmitted by a 2-bit or 3-bit A-DAI fieldincluded in a downlink grant.

The UL DAI indicates the number of downlink (E)PDCCHs indicating SPSrelease and the total number of PDSCHs scheduled by an eNB in a bundlingwindow based on at least one serving cell.

That is, the definition and the application method thereof may changebased on whether the A-DAI field is included in the downlink grant orthe uplink grant. The A-DAI may be used only for TDD UL-DLconfigurations 1 to 6, and may not be used for TDD UL-DL configuration0. Also, in the case of i) a TDD system that supports a differentTDD-UL-DL configuration for each serving cell or ii) a TDD system thatuses a DL reference UL-DL configuration for a HARQ-ACK timing in theTDD-FDD CA configuration, the DL reference UL-DL configuration mayreplace the TDD UL-DL configuration and may be used.

Unlike the semi-static HARQ-ACK codebook configuration in which the sizeof a HARQ-ACK codebook is fixed, the dynamic HARQ-ACK codebookconfiguration needs to determine the size of a HARQ-ACK codebook basedon the number of accumulated PDSCHs (A-DAD that the UE receives within abundling window and a set service cell (or CC). For example, when thenumber of accumulated PDSCHs is 2, a 2-bit HARQ-ACK is generated basedon 1 transport block (TB) per PDSCH. That is, the size of the HARQ-ACKcodebook is 2. When an eNB transmits two PDSCHs to a UE in a bundlingwindow and the UE fails to detect a PDCCH (or EPDCCH) associated with alast PDSCH (the loss of a second A-DAI), the UE recognizes that thenumber of PDSCHs is 1, generates a 1-bit HARQ-ACK, and transmits thesame to the eNB. In this instance, the size of the HARQ-ACK codebookis 1. However, the eNB expects that a HARQ-ACK is to be transmittedbased on a HARQ-ACK codebook having a size of 2 since the eNB transmitstwo PDSCHs. The HARQ-ACK that is based on a codebook having a size of 1is different from the HARQ-ACK that the eNB originally intends.

As described above, in the dynamic HARQ-ACK codebook configuration,there is a limitation in expecting the reliable size of a HARQ-ACKcodebook based on only an A-DAI. Particularly, when the UE misses thelast (E)PDCCH or PDSCH transmitted by the eNB, or when the UE misses acorresponding (E)PDCCH indicating whether 1CW is transmitted or 2CWs aretransmitted in a MIMO transmission mode, this may be a problem.

The present embodiment defines a DCI including a T-DAI so that an eNBand a UE support a reliable dynamic HARQ-ACK codebook configuration.

The T-DAI indicates the number of all PDSCHs which are scheduled inassociation with HARQ-ACK reporting of the UE. In this instance, allPDSCHs are counted over the frequency axis (set serving cells) and thetime axis (a bundling window). The T-DAI indicates the total number of(E)PDCCHs (DL assignment) indicating SPS release/associated PDSCHs basedon a current subframe. Alternatively, the T-DAI indicates the totalnumber of (E)PDCCHs (DL assignment) indicating PDSCH/SPS release withinthe set serving cells/bundling window size. Alternatively, in the abovedescribed two counting methods, the T-DAI may count the number of CWs(TBs) instead of counting the number of (E)PDCCHs indicating PDSCH/SPSrelease.

Alternatively, the T-DAI may indicate the sum of the number of (E)PDCCHsthat indicates SPS releases and the number of all PDSCHs that arescheduled in association with HARQ-ACK reporting of the UE. In thisinstance, the (E)PDCCHs indicating SPS release and all the PDSCHs may becounted over the frequency axis and the time axis.

The T-DAI is transmitted through a T-DAI field included in a downlinkgrant. The T-DAI field may be 2 bits or 3 bits. The T-DAI may be usedwhen the UE determines the size of a dynamic HARQ-ACK codebook, togetherwith the A-DAI. The A-DAI indicates the number of (E)PDCCHs indicatingSPS release and PDSCHs accumulated at each DCI transmission. Conversely,the T-DAI equally indicates the total number of (E)PDCCHs indicating SPSrelease and PDSCHs at each DCI transmission. The T-DAI prevents theconfusion that happens when obtaining the A-DAI value fails at the lasttime or serving cell, and may be helpful to improve the total DL dataperformance. Also, in the case of counting T-DAIS, a DL SPS PDSCHtransmission that is transmitted without a downlink grant (DL DCI) maybe included or may be excluded.

Here, a scheme of applying an A-DAI and/or a T-DAI and a method ofdetermining the size of a HARQ-ACK codebook may be determined to bedependent upon the number of serving cells that are available for CA andupon a duplex scheme of a serving cell through which a PUCCH istransmitted (since a HARQ-ACK transmission timing changes based onthem). They are listed up as follows.

TABLE 1 The number of serving cells FDD CA, FDD- TDD, TDD available TDDCA(PCell CA, TDD-FDD for CA Use case FDD) CA(PCell TDD) 5 or fewerDownlink No DAI field TDD UL-DL (Legacy grant configuration system, #0:no DAI field Rel. 12) TDD UL-DL configuration #1-6: time axis A-DAIfield Uplink grant No DAI field TDD UL-DL configuration #0: no DAI fieldTDD UL-DL configuration #1-6: use T-DAI field for each serving cell (orCC) Determine Semi-static Semi-static HARQ- HARQ-ACK HARQ-ACK ACKcodebook codebook size codebook configuration for PUCCH configurationDetermine Determine Use T-DAI field for HARQ-ACK HARQ-ACK each servingcell codebook size codebook size (or CC) for PUSCH for PUCCH 6 to 32Downlink Use frequency Use frequency/time (Advanced grant axis A-DAIfield axis A-DAI field system, Uplink grant — — Rel.13) DetermineSemi-static or Semi-static or static HARQ-ACK static HARQ- HARQ-ACKcodebook size ACK codebook codebook for PUCCH configurationconfiguration Determine Semi-static or Semi-static or static HARQ-ACKstatic HARQ- HARQ-ACK codebook size ACK codebook codebook for PUSCHconfiguration configuration

FIGS. 1A to 1F are diagrams illustrating an example of applying adownlink grant including an A-DAI field and a T-DAI field to an FDD orTDD PUCCH cell group according to the present disclosure.

FIGS. 1A to 1D illustrate the case in which a T-DAI indicates the numberof (E)PDCCHs indicating SPS release and/or the number of all PDSCHs thatare scheduled in the frequency axis and the time axis for apredetermined UE up to a current subframe. FIGS. 1E and 1F illustratethe case in which the T-DAI indicates the number of (E)PDCCHs indicatingSPS release and/or the number of all PDSCHs that are scheduled in thefrequency axis and the time axis for a predetermined UE throughout allsubframes.

FIG. 1A illustrate an example of a case in which an A-DAI field and aT-DAI field are included in a downlink grant in an FDD PUCCH cell group.The downlink grant in CC #0 includes A-DAI field 1 and T-DAI field 1.The downlink grant in CC#2 includes A-DAI field 2 and T-DAI field 2. Thedownlink grant in CC #4 includes A-DAI field 3 and T-DAI field 3. Thedownlink grant in CC#5 includes A-DAI field 4 and T-DAI field 4. Thedownlink grant in CC#8 includes A-DAI field 5 and T-DAI field 5.

The number of all PDSCHs that are scheduled in the frequency axis andthe time axis based on a current subframe is 5 (CC #0, #2, #4, #5, #8).Therefore, T-DAI field 1, T-DAI field 2, T-DAI field 3, T-DAI field 4,and T-DAI field 5 indicate T-DAI=5.

However, A-DAI field 1, 2, 3, 4, and 5 indicate A-DAI=1, A-DAI=2,A-DAI=3, A-DAI=4, A-DAI=5, respectively, in CC#0, #2, #4, #5, and #8.Therefore, in CC #0, #2, #4, #5, and #8, (A-DAI, T-DAI) may be given as(1, 5), (2, 5), (3, 5), (4, 5), and (5, 5), respectively.

FIG. 1B illustrates an example of a case in which an A-DAI field and aT-DAI field are included in a downlink grant in a TDD PUCCH cell group.The case corresponds to TDD and thus, it may be extended to multipledownlink subframes by a bundling window for each serving cell, and thenumber of A-DAIS accumulatively increases as a CC number increases inthe frequency axis and as a subframe number increases. Conversely, theT-DAI indicates the number of (E)PDCCHs indicating SPS release and/orthe number of all PDSCHs that are scheduled in the frequency axis andthe time axis for a predetermined UE up to a current subframe. Forexample, the total number of PDSCHs scheduled in the frequency/time axisup to a DL subframe #0 is 5 and thus, T-DAI=5 in the DL subframe #0irrespective of a CC.

The total number of PDSCHs scheduled in the frequency/time axis up to aDL subframe #1 is 8 including the previous DL subframe #0, and thus,T-DAI=8 in the DL subframe #1 irrespective of a CC. In the same manner,the total number of PDSCHs scheduled in the frequency/time axis up to aDL subframe #2 is 12 including the previous DL subframes #0 and #1, andthus, T-DAI=12 in the DL subframe #2, irrespective of a CC. The totalnumber of PDSCHs scheduled in the frequency/time axis up to a DLsubframe #3 is 16 including the previous DL subframes #0, #1, and #2,and thus, T-DAI=16 in the DL subframe #3, irrespective of a CC.

Referring to FIG. 1C, it is the case in which some CCs are set to a MIMOmode and 2TBs per CC are possible. In FIG. 1C, CC #0, #2, and #4 are setto a MIMO mode, and only CC#0 and CC#2 allow a 2TBs-per-CC transmission,and the remaining CCs allow a 1 TB-per-CC transmission.

The number of CWs(TBs) in all the PDSCHs that are scheduled in thefrequency axis and the time axis based on a current subframe is 7 (2(CC#0)+2(CC #2)+1(CC #4), 1(CC #5)+1(CC #8)). Therefore, all of the T-DAIfields that are transmitted in each CC in a current subframe indicateT-DAI=7. That is, A-DAI/T-DAI fields in a downlink grant executecounting based on a CW(TB) unit, as opposed to a PDSCH transmissionunit. An (E)PDCCH transmission indicating DL SPS release may be alwayscounted based on 1 CW.

In the case of 2TBs-per-CC, a PDSCH including two CWs(TBs) istransmitted in a corresponding CC and thus, the number of A-DAIsincreases by 2 for each PDSCH (or serving cell) when the number ofA-DAIs is counted based on a CW unit. A HARQ-ACK therefore requires 2bits, and thus, the size of a HARQ-ACK codebook increases by 2.Therefore, in FIG. 1C, (A-DAI, T-DAI) may be (2, 7) and (4, 7) in CC #0and #2, and (A-DAI, T-DAI) may be (5, 7), (6, 7), and (7, 7) in CC #4,#5, and #8.

Referring to FIG. 1D, it is the case in which some CCs are set to a MIMOmode and 2TBs per CC are possible. In FIG. 1D, CC #0, #1, and #2 are setto a MIMO mode, and only CC#0 and CC#1 allow a 2TBs-per-CC transmission,and the remaining CCs allow a 1 TB-per-CC transmission. In the samemanner as FIG. 1C, FIG. 1D illustrates an example of executing DAIcounting based on a CW unit.

Also, TDD is a PUCCH serving cell and thus, it can be extended tomultiple downlink subframes by a bundling window, and the number ofA-DAIs accumulatively increases as a CC number increases in thefrequency axis, and subsequently, as a subframe number increases.Conversely, the T-DAI indicates the number of (E)PDCCHs indicating SPSrelease and/or the number of all PDSCHs that are scheduled in thefrequency axis and the time axis for a predetermined UE up to a currentsubframe. For example, the total number of PDSCHs scheduled in thefrequency/time axis up to a DL subframe #0 is 6 by taking intoconsideration 2TBs (CWs) in CC#0, and thus, T-DAI=6 in the DL subframe#0, irrespective of a CC. Therefore, in DL subframe #0, (A-DAI, T-DAI)of CC #0 may be (2, 6), and (A-DAI, T-DAI) may be (3, 6), (4, 6), (5,6), and (6, 6) in CC #2, #4, #5, and #8, respectively.

The total number of PDSCHs scheduled in the frequency/time axis up to aDL subframe #1 is 10 including the previous DL subframe #0 and thus,T-DAI=10 in the DL subframe #1, irrespective of a CC. In the samemanner, the total number of PDSCHs scheduled in the frequency/time axisup to a DL subframe #2 is 14 including the previous DL subframes #0 and#1, and thus, T-DAI=14 in the DL subframe #2, irrespective of a CC.

FIG. 1E and FIG. 1F illustrate the case in which the T-DAI indicates thenumber of (E)PDCCHs indicating SPS release and/or the number of allPDSCHs that are scheduled in the frequency axis and the time axis for apredetermined UE throughout all subframes in a bundling window.Therefore, FIG. 1E shows that the T-DAI is fixed to 16 (T-DAI=16)throughout all subframes and CCs where PDSCHs are scheduled. FIG. 1Fshows that the T-DAI is fixed to 19 (T-DAI=19) throughout all subframesand CCs where PDSCHs are scheduled. In FIG. 1E, counting is performedbased on the number of (E)PDCCHs indicating DL SPS release and PDSCHs.Also, FIG. 1E is the case in which MIMO is not set, and FIG. 1Fillustrates the case in which MIMO is set for some CCs and the number ofA-DAIs and the number of T-DAIs are counted based on a CW(TB).Therefore, in FIG. 1F, the number of A-DAIs may increase by 2 in CC #0and CC#1.

Hereinafter, embodiments in which a UE dynamically determines the sizeof a HARQ-ACK codebook based on an A-DAI and a T-DAI will be disclosed.Particularly, the present embodiments will be described under theassumption of the case in which HARQ-ACK reporting with respect to adownlink data (PDSCH) transmission of a previous subframe of a currentsubframe needs to be transmitted in parallel with an uplink data (PUSCH)transmission in the current subframe that needs to perform the uplinkdata (PUSCH) transmission. However, the present embodiments may beequally applied when HARQ-ACK reporting is performed based on a PUCCHformat.

[Case 1] Determination Based on a Downlink Grant Including a T-DAI Field

The case may occur in which a PUSCH transmission indicated by a previoussubframe (e.g., subframe n−4 in FDD PUCCH cell group, subframe n−k inTDD PUCCH cell group) of a current subframe (e.g., subframe n) may betransmitted together with HARQ-ACK information with respect to an(E)PDCCH indicating a SPS release and a PDSCH, which is transmitted inthe previous subframe (e.g., subframe n−4 in FDD PUCCH cell group,subframe n−k in TDD PUCCH cell group).

In this instance, a UE may determine (or calculate) the size of aHARQ-ACK codebook with respect to the (E)PDCCH that indicates SPSrelease and a PDSCH transmitted over at least one serving cell, based onthe T-DAI field included in a downlink grant. Two embodiments will bedisclosed in association with the method of determining the size of aHARQ-ACK codebook based on a T-DAI field.

First Embodiment Determining the Size of a HARQ-ACK Codebook Based on aT-DAI that is Actually Allocated to a UE

According to the present embodiment, a UE determines a T-DAI that isactually allocated to the UE based on an A-DAI field and a T-DAI field.

Here, the value of a single T-DAI field may correspond to a plurality ofT-DAIs (that is, a T-DAI set). In other words, a plurality of T-DAIs maybe indicated by a single T-DAI field value. For example, when a T-DAIfield is 2 bits as shown in following Table 2, the T-DAI field has fourvalues X_(DAI) ^(total), that is, 00, 01, 10, and 11, and a single valuemay be mapped to a plurality of T-DAIS.

TABLE 2 T-DAI field (MSB, T-DAI LSB) X_(DAI) ^(total) set correspondingto T-DAI field 0, 0 1 1, 5, 9, 13, 17, 21, 25, 29 0, 1 2 2, 6, 10, 14,18, 22, 26, 30 1, 0 3 3, 7, 11, 15, 19, 23, 27, 31 1, 1 4 0, 4, 8, 12,16, 20, 24, 28, 32

Referring to Table 2, when X_(DAI) ^(total), a T-DAI that is actuallyallocated to a UE may be one of the values in the set {1, 5, 9, 13, 17,21, 25, 29}. According to the scheme, a T-DAI may be indicated byminimizing the number of bits of the T-DAI field added to a DCI format.This is possible through the assumption that a probability ofsuccessively missing four (E)PDCCHs (assuming a 2-bit T-DAI field) issignificantly low. A UE may derive a T-DAI that is actually allocated tothe UE by taking into consideration a received A-DAI field and T-DAIfield in a single bundling window (on a plurality of serving cells (orCCs) in a single subframe in the case of FDD, and on a plurality ofserving cells (or CCs) in a plurality of subframes in the case of TDD).

For example, when a T-DAI field is 0,0 in Table 2, a latent T-DAIcorresponds to {1, 5, 9, 13, 17, 21, 25, 29} and a UE derives one as anactually allocated T-DAI by taking into consideration an A-DAI value. Itis assumed that a T-DAI field in a downlink grant that the UE receivesis 0,0, and an A-DAI in a downlink grant that the UE receives in thelast subframe is 4 (A-DAI=4). However, 4 does not exist in the T-DAI set{1, 5, 9, 13, 17, 21, 25, 29}. Therefore, the UE regards 5 which is theclosest among the set {1, 5, 9, 13, 17, 21, 25, 29} as a T-DAI that isactually allocated to the UE. The UE determines that one PDCCH is lost.

Subsequently, the UE sets, as a NACK, a HARQ-ACK with respect to a PDSCHcorresponding to A-DAI=5, and calculates the size of a HARQ-ACK codebookbased on “T-DAI=5”.

Table 3 shows an example in which a single T-DAI field value correspondsto a plurality of T-DAIS when a T-DAI field is 3 bits.

TABLE 3 T-DAI field (MSB, T-DAI LSB) X_(DAI) ^(total) set correspondingto T-DAI field 0, 0, 0 1 1, 9, 17, 24, 32 0, 0, 1 2 2, 10, 18, 25 0, 1,0 3 3, 11, 19, 26 0, 1, 1 4 4, 12, 20, 27 1, 0, 0 5 5, 13, 21, 28 1, 0,1 6 6, 14, 22, 29 1, 1, 0 7 7, 15, 23, 30 1, 1, 1 8 0, 8, 16, 24, 31

Referring to Table 3, when X_(DAI) ^(total), a T-DAI that is actuallyallocated to a UE may be one of the values in the set {1, 9, 17, 24,32}. A method of deriving a T-DAI that is actually allocated to the UEis the same as the descriptions provided with reference to Table 2.

When the T-DAI that is actually allocated to the UE is determined, theUE may determine or calculate the size of a HARQ-ACK codebook based onthe determined T-DAI and the number of bits (1 or 2) of a HARQ-ACK withrespect to a PDSCH which is determined for each serving cell.

When counting the number of bits of a HARQ-ACK with respect to a PDSCHwhich is set for each serving cell and T-DAI counting is performed basedon a codeword (CW) unit, the UE may use a T-DAI that is determined basedon an A-DAI field and a T-DAI field as the size of a HARQ-ACK codebook.

When counting the number of bits of a HARQ-ACK with respect to a PDSCHwhich is set for each serving cell and when T-DAI counting is performedbased on a PDSCH unit, the UE may not be aware of the actual number ofCWs (or TBs) with respect to a missing PDSCH in a serving cell set to aMIMO transmission mode. Therefore, the UE may calculate the size of aHARQ-ACK codebook by assuming that the number of bits of a HARQ-ACK inthe MIMO transmission mode is fixed in advance.

As an example of a fixed number of bits, a HARQ-ACK corresponding to asingle A-DAI field may be fixed to 1 bit under the assumption thatspatial bundling is applied to all serving cells. Under the assumptionthat a HARQ-ACK with respect to a missing PDSCH is 1 bit, the UEcalculates the size of a HARQ-ACK codebook based on the determinedT-DAI. The UE generates a 1-bit HARQ-NACK based on the fixed number ofbits with respect to the missing PDSCH.

As another example of the fixed number of bits, a HARQ-ACK correspondingto a single A-DAI field may be fixed as 2 bits per CC, with respect to aserving cell that is set to an MIMO transmission mode. In this instance,the number of CWs that are actually scheduled to a PDSCH on a servingcell that is set to the MIMO is not considered. The UE may calculate thesize of a HARQ-ACK codebook based on the determined T-DAI, under theassumption that a HARQ-ACK with respect to a missing PDSCH in a servingcell set to MIMO misses is 2 bits. The UE generates a 2-bit HARQ-NACKbased on the fixed number of bits with respect to the missing PDSCH.

Second Embodiment Determining the Size of a HARQ-ACK Codebook Based onthe Value of a Received T-DAI Field

The present embodiment is a method of determining the size of a HARQ-ACKcodebook assuming a situation in which an FDD PUCCH cell group isapplied. When a PUSCH transmission is performed based on a received(E)PDCCH (DCI format 0 or 4), a UE determines the size of a HARQ-ACKcodebook based on the value of a T-DAI field, and performs a HARQ-ACKtransmission. To this end, the UE according to the present embodimentmay calculate the total number of scheduled serving cells (or CCs).

An example of a method of calculating the total number of scheduledserving cells (or CCs) is as shown in Equation 1 provided below.

B ^(DL) =X _(DAI) ^(total)+┌(D−X _(DAI)^(total))/2^(k)┐·2^(k)  [Equation 1]

Referring to Equation 1, B^(DL) indicates the number of CWs or thenumber of serving cells that require HARQ-ACK reporting out of the totalserving cells. For example, when a PUSCH is transmitted in subframe n,B^(DL) indicates the number of CWs or the number of serving cells (or DLCCs) that require HARQ-ACK reporting in subframe n−4 in the case of anFDD PUCCH cell.

In the case in which B^(DL) is calculated as the number of serving cells(or DL CCs), the number of HARQ-ACK bits may be assumed as follows: i) a1-bit HARQ-ACK always corresponds each serving cell by applying spatialbundling to a corresponding serving cell when a 2 TB transmission modeis set to the serving cell. ii) when a 1 TB transmission mode is set toa serving cell, 1 bit per CC is assumed without the application ofspatial bundling.

Referring again to Equation 1, X_(DAI) ^(total) is the value of a T-DAIfield, and the value may be 1 to 2^(k) based on the number of bits.Here, when a T-DAI field is 2 bits or 3 bits, a T-DAI set, such as thosein Table 2 or Table 3, may correspond to the T-DAI field.

D denotes the number of CWs or the number of serving cells including an(E)PDCCH that indicates SPS release and a PDSCH received by a UE, out ofthe total serving cells configured for the UE.

X_(DAI) ^(total) and D may be counted based on an (E)PDCCH unit thatindicates DL SPS release/a PDSCH, or may be counted based on a CW unit.In any case, the same counting scheme should be applied to both X_(DAI)^(total) and D. An example of calculating the size of a HARQ-ACKcodebook based on Equation 1 is the same as FIG. 2.

FIG. 2 is a diagram illustrating a method of calculating the size of aHARQ-ACK codebook according to the second embodiment.

FIG. 2 assumes a case in which an FDD PUCCH cell and 12 serving cells(or CCs) are set for a UE, and DL scheduling (or assignment) isindicated by an eNB for each serving cell in subframe n−4, as shown inFIG. 2, and a PUSCH transmission in subframe n (HARQ-ACK transmissiontiming) is indicated by an uplink grant. Also, it is assumed that T-DAIcounting is performed based on an (E)PDCCH unit that indicates DL SPSrelease/a PDSCH unit.

When an eNB sets a T-DAI field (2 bits) in a downlink grant to “10” andtransmits the downlink grant to a UE, X_(DAI) ^(total)=3 may beindicated to the UE by the eNB.

When the UE misses a DL assignment corresponding to serving cell #9, D=6which is the total accumulative number of (E)PDCCHs indicating DL SPSrelease/PDSCHs received by the UE. In this instance, the size of aHARQ-ACK codebook that piggybacks on a PUSCH isB^(DL)=3+celing{(6−3)/2²}0.2²=7, based on Equation 2. Here, the UE mayrecognize whether DL scheduling of serving cell #9 misses based on a DLA-DAI and/or other recognition schemes.

FIG. 3 is a diagram illustrating a method for determining the size of aHARQ-ACK codebook when a DL SPS PDSCH transmission exists according toan example of the present invention.

Referring to FIG. 3, when HARQ-ACK bits that need to be transmitted on acorresponding PUSCH are associated with a DL SPS PDSCH, in addition toan (E)PDCCH indicating SPS release and/or a PDSCH indicated by at leastone downlink grant, the eNB increases a count by 1 in addition to the(E)PDCCH indicating DL SPS release and a PDSCH transmission indicated bythe downlink grant by taking into consideration the DL SPS PDSCHtransmission when setting a T-DAI.

In FIG. 3, the total number (T-DAI=12) is 12 when only PDSCHs arecounted throughout DL subframes #0, #1, #2, and #3 and serving cells #0,#2, #4, #5, and #8. However, a DL SPS PDSCH exists, and thus a T-DAIcount is increased by 1 and is set to T-DAI=13.

FIG. 4 is a diagram illustrating a method of determining the size of aHARQ-ACK codebook when a DL SPS PDSCH transmission exists according toanother example of the present invention.

Referring to FIG. 4, a DL SPS PDSCH is excluded when a T-DAI is set.That is, an eNB sets a T-DAI based on only the number of (E)PDCCHsindicating SPS release and PDSCHs indicated by (E)PDCCHs. A UE and aneNB determines the final size of a HARQ-ACK codebook by adding

to the size of a HARQ-ACK codebook calculated based on the T-DAI. Here,

has 1 when a DL SPS PDSCH transmission exists. Otherwise, it has 0.

When only HARQ-ACK information corresponding to a DL SPS PDSCHtransmission needs to be transmitted through a PUSCH, a UE may not beable to determine an A-DAI field and a T-DAI field due to the lack of adownlink grant. Accordingly, when a DL SPS PDSCH is received, the UEregards

=1 as the final size of a HARQ-ACK codebook, and performs a HARQ-ACKtransmission.

In Case 1, a UE derives the size of a HARQ-ACK codebook on a PUSCH basedon an A-DAI field and a T-DAI field included in a downlink grant andthus, including a T-DAI field in an uplink grant is not considered. As amatter of course, a DAI field may exist in an uplink grant in a TDDsystem. Accordingly, the function of the DAI field of the legacy TDDsystem may be equally applied. This may be listed in a table as providedbelow.

TABLE 4 Uplink grant format Cell group Downlink grant format Option 1Option 2 FDD PUCCH Including A-DAI field No DAI No DAI Cell group andT-DAI field field field TDD PUCCH Including A-DAI field No DAI LegacyDAI Cell group and T-DAI field field field

[Case 2] Determination Based on a Downlink Grant Including a T-DAI Fieldand an Uplink Grant Including a T-DAI Field

The case may occur in which a PUSCH transmission indicated by a previoussubframe (e.g., subframe n−4 in FDD PUCCH cell, subframe n−k in TDDPUCCH cell) of a current subframe (e.g., subframe n) may be transmittedtogether with HARQ-ACK information with respect to an (E)PDCCHindicating SPS release and a PDSCH transmitted in the previous subframe(e.g., subframe n−4 in FDD PUCCH cell group, subframe n−k in TDD PUCCHcell group).

In this instance, a UE may determine (or calculate) the size of aHARQ-ACK codebook with respect to the (E)PDCCH that indicates SPSrelease and an a PDSCH transmitted over at least one serving cell basedon a DL T-DAI field included in the downlink grant and a UL T-DAI fieldincluded in the uplink grant.

That is, unlike Case 1, in Case 2 both an uplink grant and a downlinkgrant include a T-DAI field. By including a T-DAI field in an uplinkgrant, double checking is possible when using only a downlink grant isinsufficient to secure reliability in determining the size of a HARQ-ACKcodebook. According to Case 2, a T-DAI field may be included in theuplink grant and thus, Table 4 may be modified to Table 5, as providedbelow.

TABLE 5 Cell downlink grant uplink grant format group format Option 1Option 2 Option 3 Option 4 FDD Including A- Including Including ULIncluding No DAI field PUCCH DAI field and UL T-DAI T-DAI UL T-DAI cellgroup DL T-DAI field field field field TDD Including A- IncludingSwitching Including Switching PUCCH DAI field and UL T-DAI between UL T-legacy DAI between UL T- cell group DL T-DAI field field DAI field andfield DAI field and legacy DAI legacy DAI field is possible field ispossible

Referring to Table 5, Case 2 proposes a method of determining the sizeof a HARQ-ACK codebook when an A-DAI field and a DL T-DAI field areincluded in a downlink grant (i.e., DCI format 1/1A/1B/1D/2/2A/2B/2C/2D)as well as when a UL T-DAI field and/or legacy TDD DAI field is includedin an uplink grant (i.e., DCI format 0/4) (Option 1 to 4). Here, a DLT-DAI field and a UL T-DAI field are differentiated so as to distinguishthe case when the T-DAI field is included in a downlink grant from thecase when substantially the same T-DAI field is included in an uplinkgrant, and they are equally called “T-DAI field”.

A eNB redundantly transmits a T-DAI field through an uplink grant inaddition to a downlink grant since it is difficult to exclude the casein which a UE fails to receive an actually allocated T-DAI. For example,when a small number of downlink grants are scheduled in a servingcell/bundling window (only TDD), a UE may fail to receive all of thedownlink grants. Also, in an LAA environment, when a prepared (E)PDCCHis not normally transmitted and is dropped due to the failure of an LBT,a plurality of DAI values may not be transmitted to the UE(particularly, a transmission corresponding to consecutive (E)PDCCHs),and thus, the UE may be confused in association with an actual DAIvalue. Since the number of bits of a DAI field is limited to 2 to 3,ambiguity may be caused when a modulo operation reaches its limitation.For example, in the case of a 2-bit DAI field, when four consecutive(E)PDCCHs are missed, the modulo operation may not be normallyperformed.

Under the situation, to accurately obtain the size of a HARQ-ACKcodebook, an eNB may transmit an uplink grant including a UL T-DAI fieldto a UE according to the embodiment of Case 2.

Third Embodiment

When a PUSCH transmission is indicated by an (E)PDCCH (DCI format 0/4),a UE may determine the size of an entire HARQ-ACK codebook based onmethods of Option 1 to 4, and may perform a HARQ-ACK transmission.

For example, according to Option 1, a UL T-DAI field is included in anuplink grant. Therefore, a UE calculates the size of a HARQ-ACK codebookon a PUSCH based on a UL T-DAI field. In this instance, the UE mayderive a T-DAI that is actually allocated to the UE based on the ULT-DAI field. The method that is the same as in Case 1 may be used. Here,when the size of a HARQ-ACK codebook calculated based on a DL T-DAI andthe size of a HARQ-ACK codebook calculated based on a UL T-DAI aredifferent from each other, the UE determines this as an erroneoussituation, and determines the size of a HARQ-ACK codebook based on onethat is most recently received out of the DL T-DAI and the UL T-DAI.Alternatively, when the DL T-DAI and the UL T-DAI are received in thesame subframe recently and the values are different, the UE determinesthe size of a HARQ-ACK codebook based on one of the DL T-DAI and the ULT-DAI. Alternatively, the UE always determines the size of a HARQ-ACKcodebook based on the UL T-DAI value.

As another example, according to Option 2, although a UL T-DAI field isused for an FDD PUCCH cell group, a legacy DAI field and a T-DAI fieldare selectively used for a T PUCCH cell group. In this instance, astandard for determining a field to be used may be based on a TDD UL-DLconfiguration of a TDD PUCCH cell group. For example, when a TDD PUCCHcell group is TDD UL-DL configuration #5, a T-DAI field is used. Whenother TDD UL-DL configurations are used, a legacy DAI field may be used,as opposed to a T-DAI field.

As another example, according to Option 3 a UL T-DAI field is not usedfor a TDD PUCCH cell group, and the UE may determine the size of aHARQ-ACK codebook by reusing a legacy DAI field. This case is differentfrom the case of an FDD PUCCH cell group which uses a T-DAI field.

As another example, according to Option 4, an uplink grant associatedwith an FDD PUCCH cell group does not need any DAI field, and an uplinkgrant associated with a TDD PUCCH cell group may selectively include alegacy DAI field or a UL T-DAI field. For example, a standard fordetermining a field to be used may be based on a TDD UL-DL configuration(or DL reference UL-DL configuration) of a TDD PUCCH cell group. Asanother example, by adding a 1-bit indication field associated with aDAI configuration in a DCI format, it may be indicated to a UE whether acorresponding DAI field is a UL T-DAI field or a legacy DAI field.

Fourth Embodiment

When a PUSCH transmission is not indicated by an (E)PDCCH (DCI format0/4), a UE may determine the size of an entire HARQ-ACK codebook basedon methods of Alt 1 to 3, and may perform a HARQ-ACK transmission. Alt 1to 3 are methods of determining the size of a HARQ-ACK, particularlywhen a UE fails to receive a T-DAI field from both a downlink grant andan uplink grant.

For example, according to Alt 1, a T-DAI is determined based on B^(DL)=#of configured CCs*2. This assumes that 2TBs are transmitted through aPDSCH for each serving cell, irrespective of a transmission mode set foreach serving cell. This assumption complies with the case in which T-DAIcounting is performed based on the number of TBs (CWs) when a PUSCHtransmission is indicated by an uplink grant.

As another example, according to Alt 2, a T-DAI is determined based onB^(DL)=# of configured CCs. This assumes that 1 TB is always transmittedthrough a PDSCH for each serving cell, irrespective of a transmissionmode set for each serving cell. This assumption complies with the casein which T-DAI counting is performed based on the number of CCs when aPUSCH transmission is indicated by an uplink grant.

As another example, according to Alt 3, a UE determines B^(DL) based ona DAI value (a value accumulated in a CC area at each scheduling)counted based on information included in a downlink grant and the sizeof a HARQ-ACK codebook on a PUSCH. Here, additional informationassociated with the size of a HARQ-ACK codebook may be information thatan eNB provides to a UE or a UE provides to an eNB, to solve a loss of aDL assignment having a DAI field. For example, the value indicated by aDAI field corresponding to the lowest index may be a T-DAI. Therefore,an additional T-DAI field may not need to be included in an (E)PDCCH.

FIG. 5 is a flowchart illustrating a method for a UE to transmit aHARQ-ACK according to an example of the present disclosure. This is thecase in which a T-DAI field is included in only a downlink grantaccording to Case 1.

Referring to FIG. 5, a UE receives, from an eNB, a downlink grantincluding a T-DAI field on a PDCCH in operation S500. Before operationS500, the UE may receive, from the eNB, information indicating theconfiguration of a semi-static HARQ-ACK codebook or a dynamic HARQ-ACKcodebook. The semi-static HARQ-ACK codebook configuration is a firstmode that the eNB transmits, to the UE, a higher layer signalingassociated with the size of a HARQ-ACK codebook. The dynamic HARQ-ACKcodebook configuration is a second mode that the eNB does not transmit,to the UE, a higher layer signaling associated with the size of aHARQ-ACK codebook. In the second mode, the UE may determine a T-DAI andthe size of a HARQ-ACK codebook based on an A-DAI field and a T-DAIfield.

The UE receives, from the eNB, a PDSCH indicated by the PDCCH inoperation S505. As many PDSCHs as a value corresponding to a T-DAI maybe transmitted in the time axis (at least one subframe) or the frequency(at least one serving cell or CC) in a given bundling window.

The UE receives an uplink grant indicating a PUSCH transmission from theeNB on an (E)PDCCH in operation S510. The downlink grant in operationS500 and the uplink grant in operation S510 may be received in the samesubframe n. Also, the PUSCH may be transmitted in a subsequent subframe(e.g., subframe n+4 in FDD PUCCH cell, subframe n+k in TDD PUCCH cell)together with HARQ-ACK information with respect to the PDCCH indicatingthe PDSCH. Alternatively, the PUSCH may be transmitted together withHARQ-ACK information with respect to an (E)PDCCH indicating SPS releaseand the PDSCH.

A T-DAI field may correspond to a T-DAI set. For example, when the T-DAIfield is 2 bits, Table 2 may be used. When the T-DAI field is 3 bits,Table 3 may be used. The UE determines a T-DAI that is actuallyallocated to the UE from the T-DAI set in operation S515. To this end,an A-DAI field and a T-DAI field may be used. The method of determininga T-DAI that is actually allocated to the UE in operation S515 mayinclude the methods of determining a T-DAI, which have been described inCase 1.

The UE determines the size of a HARQ-ACK codebook in operation S520. Themethod in which the UE calculates the size of a HARQ-ACK codebook inoperation S520 may include the methods of calculating the size of aHARQ-ACK codebook, which have been described in Case 1.

The UE generates a HARQ-ACK based on whether decoding (E)PDCCHsindicating DL SPS release/PDSCHs corresponding to a T-DAI aresuccessfully decoded in operation S525. When ACKs or NACKs with respectto (E)PDCCHs indicating DL SPS release/PDSCHs corresponding to a T-DAIare transmitted on a single associated PUSCH, the UE matches acombination of ACKs and NACKs with respect to the (E)PDCCHs indicatingDL SPS release/PDSCHs corresponding to T-DAI to a single code includedin a HARQ-ACK codebook having the calculated size, thereby generating aHARQ-ACK. Here, the UE may generate a NACK with respect to an (E)PDCCHor a PDSCH that the UE misses. Detailed operations thereof include themethod of generating a HARQ-ACK with respect to a missing PDCCH or PDSCHin Case 1 and Case 2.

The UE transmits the generated HARQ-ACK to the eNB on a PUSCH in asubsequent subframe (e.g., subframe n+4 in FDD PUCCH cell group,subframe n+k in TDD PUCCH cell group) in operation S530.

FIG. 6 is a flowchart illustrating a method for a UE to transmit aHARQ-ACK according to another example of the present invention. This isthe case in which a T-DAI field is included in both a downlink grant andan uplink grant according to Case 2.

Referring to FIG. 6, a UE receives, from an eNB a downlink grantincluding an A-DAI field and a DL T-DAI field and an uplink grantincluding a UL T-DAI field on different (E)PDCCHs in operation S600.According to Case 2, based on Options, the uplink grant may include alegacy DAI field instead of a UL T-DAI field (refer to Table 5).

Before operation S600, the UE may receive, from the eNB, informationindicating the configuration of a semi-static HARQ-ACK codebook or adynamic HARQ-ACK codebook. The semi-static HARQ-ACK codebookconfiguration is a first mode that the eNB transmits, to the UE, ahigher layer signaling associated with the size of a HARQ-ACK codebook.The dynamic HARQ-ACK codebook configuration is a second mode that theeNB does not transmit, to the UE, a higher layer signaling associatedwith the size of a HARQ-ACK codebook. In the second mode, the UE maydetermine a final T-DAI and the size of a HARQ-ACK codebook based on anA-DAI field, a DL T-DAI field, and a UL T-DAI field.

The UE receives, from the eNB, a PDSCH indicated by the PDCCH inoperation S605. As many PDSCHs as a value corresponding to the finalT-DAI may be transmitted in the time axis (at least one subframe) or thefrequency axis (at least one serving cell or CC) in a given bundlingwindow.

The UE receives an uplink grant indicating the transmission of a PUSCHfrom the eNB on a PDCCH in operation S610. The uplink grant in operationS600 and the uplink grant in operation S610 may be the same as ordifferent from each other. According to the former case, the downlinkgrant in operation S600 and the uplink grant in operation S610 may bereceived in the same subframe n. Also, the PUSCH may be transmitted in asubsequent subframe (e.g., subframe n+4 in FDD PUCCH cell group,subframe n+k in TDD PUCCH cell group) together with HARQ-ACK informationwith respect to the PDCCH indicating the PDSCH. Alternatively, the PUSCHmay be transmitted together with HARQ-ACK information with respect to an(E)PDCCH indicating SPS release and the PDSCH.

A T-DAI field may correspond to a T-DAI set. For example, when the T-DAIfield is 2 bits, Table 2 may be used. When the T-DAI field is 3 bits,Table 3 may be used. The UE determines a DL T-DAI based on the DL T-DAIfield, and determines a UL T-DAI based on the UL T-DAI field inoperation S615. The method of determining the DL T-DAI and the UL T-DAIin operation S615 may include the methods of determining a T-DAI, whichhave been described in Case 1.

The UE determines the size of a HARQ-ACK codebook based on the finalT-DAI in operation S620. Operation S620 includes: an operation comparingthe DL T-DAI and the UL T-DAI by the UE; an operation determining thefinal T-DAI based on the result of the comparison; and an operationcalculating the size of a HARQ-ACK codebook based on the A-DAI and thefinal T-DAI. Operation S620 may include the methods of calculating thesize of a HARQ-ACK codebook which have been described in Case 2.Alternatively, the UE determines the size of the entire HARQ-ACKcodebook based on Alt 1 to 3 methods of Case 2, and performs a HARQ-ACKtransmission.

The UE generates a HARQ-ACK based on whether PDSCHs corresponding to thefinal T-DAI are successfully decoded in operation S625. When ACKs orNACKs with respect to PDSCHs corresponding to the final T-DAI aretransmitted on a single associated PUSCH, the UE matches a combinationof ACKs and NACKs with respect to the PDSCHs corresponding to the finalT-DAI to a single code included in a HARQ-ACK codebook having thecalculated size, thereby generating a HARQ-ACK. Here, the UE maygenerate a NACK with respect to a PDCCH or PDSCH that the UE misses.Detailed operations thereof include the method of generating a HARQ-ACKwith respect to a missing PDCCH or PDSCH in Case 1 and Case 2.

The UE transmits the generated HARQ-ACK to the eNB on a PUSCH in asubsequent subframe (e.g., subframe n+4 in FDD, subframe n+k in TDD) inoperation S630.

FIG. 7 is a flowchart illustrating a method for an eNB to receive aHARQ-ACK according to an example of the present invention. This is thecase in which a T-DAI field is included in only a downlink grantaccording to Case 1.

Referring to FIG. 7, an eNB sets an A-DAI and a T-DAI and transmits adownlink grant, including an A-DAI field indicating the set A-DAI and aT-DAI field indicating the set T-DAI, to a UE on a PDCCH in operationS700. Before operation S700, the eNB may transmit, to the UE,information indicating the configuration of a semi-static HARQ-ACKcodebook or a dynamic HARQ-ACK codebook. The semi-static HARQ-ACKcodebook configuration is a first mode that the eNB transmits, to theUE, a higher layer signaling associated with the size of a HARQ-ACKcodebook. The dynamic HARQ-ACK codebook configuration is a second modethat the eNB does not transmit, to the UE, a higher layer signalingassociated with the size of a HARQ-ACK codebook. In the second mode, theUE may determine a T-DAI and the size of a HARQ-ACK codebook based on anA-DAI field and a T-DAI field.

The eNB transmits, to the UE, a PDSCH indicated by the PDCCH inoperation S705. As many PDSCHs as a value corresponding to a T-DAI maybe transmitted in the time axis (at least one subframe) or the frequency(at least one serving cell or CC) in a given bundling window.

The eNB transmits an uplink grant indicating a PUSCH transmission to theUE on a PDCCH in operation S710. The downlink grant in operation S700and the uplink grant in operation S710 may be transmitted in the samesubframe n. Also, the PUSCH may be transmitted in a subsequent subframe(e.g., subframe n+4 in FDD PUCCH cell group, subframe n+k in TDD PUCCHcell group) together with HARQ-ACK information with respect to the PDCCHindicating the PDSCH. Alternatively, the PUSCH may be transmittedtogether with HARQ-ACK information with respect to an (E)PDCCHindicating SPS release and the PDSCH.

A T-DAI field may correspond to a T-DAI set. For example, when the T-DAIfield is 2 bits, Table 2 may be used. When the T-DAI field is 3 bits,Table 3 may be used.

The eNB receives the HARQ-ACK from the UE on a PUSCH in a subsequentsubframe (e.g., subframe n+4 in FDD PUCCH cell group, subframe n+k inTDD PUCCH cell group) in operation S715.

FIG. 8 is a flowchart illustrating a method for an eNB to receive aHARQ-ACK according to another example of the present invention. This isthe case in which a T-DAI field is included in both a downlink grant andan uplink grant according to Case 2.

Referring to FIG. 8, an eNB sets an A-DAI, a DL T-DAI, and a UL T-DAI,and transmits a downlink grant (including an A-DAI field indicating anA-DAI and a DL T-DAI field indicating a DL T-DAI) and an uplink grant(including an UL T-DAI field indicating UL T-DAI) to a UE on differentPDCCHs or the same PDCCH in operation S800. According to Case 2, basedon Options, the uplink grant may include a legacy DAI field instead ofan UL T-DAI field (refer to Table 5).

Before operation S800, the eNB may transmit, to the UE, informationindicating the configuration of a semi-static HARQ-ACK codebook or adynamic HARQ-ACK codebook. The semi-static HARQ-ACK codebookconfiguration is a first mode that the eNB transmits, to the UE, ahigher layer signaling associated with the size of a HARQ-ACK codebook.The dynamic HARQ-ACK codebook configuration is a second mode that theeNB does not transmit, to the UE, a higher layer signaling associatedwith the size of a HARQ-ACK codebook. In the second mode, the UE maydetermine a final T-DAI and the size of a HARQ-ACK codebook based on anA-DAI field, a DL T-DAI field, and a UL T-DAI field.

The eNB transmits, to the UE, a PDSCH indicated by the PDCCH inoperation S805. As many PDSCHs as a value corresponding to the finalT-DAI may be transmitted in the time axis (at least one subframe) or thefrequency (at least one serving cell or CC) in a given bundling window.

The eNB transmits an uplink grant indicating a PUSCH transmission to theUE on a PDCCH in operation S810. The uplink grant in operation S800 andthe uplink grant in operation S810 may be the same as, or different fromeach other. According to the former case, the downlink grant inoperation S800 and the uplink grant in operation S810 may be received inthe same subframe n. Also, the PUSCH may be transmitted in a subsequentsubframe (e.g., subframe n+4 in FDD, subframe n+k in TDD) together withHARQ-ACK information with respect to the PDCCH indicating the PDSCH.Alternatively, the PUSCH may be transmitted together with HARQ-ACKinformation with respect to an (E)PDCCH indicating SPS release and thePDSCH.

A T-DAI field may correspond to a T-DAI set. For example, when the T-DAIfield is 2 bits, Table 2 may be used. When the T-DAI field is 3 bits,Table 3 may be used.

The eNB receives the HARQ-ACK from the UE on a PUSCH in a subsequentsubframe (e.g., subframe n+4 in FDD, subframe n+k in TDD) in operationS815.

FIG. 9 is a block diagram illustrating a UE and an eNB according to anexample of the present disclosure.

Referring to FIG. 9, a UE 900 calculates the size of HARQ-ACK codebook,generates a HARQ-ACK, and transmits the HARQ-ACK according to Case 1 andCase 2 disclosed in the present specification. Also, an eNB 950 performsoperations in response to the operations of UE 900 according to Case 1and Case 2 disclosed in the present specification.

For example, an RF circuit 920 transmits a HARQ-ACK to the eNB 950, orreceives, from the eNB 950, a downlink grant including an A-DAI fieldand a T-DAI field, an uplink grant including a T-DAI field, or a PDSCH,PDCCH, a higher layer signaling, or the like.

Particularly, a processor 910 of the UE 900 may decode and interpret thereceived downlink grant, uplink grant, PDCCH, PDSCH, higher layersignaling, or the like, and may generate and transmit a HARQ-ACK basedon the decoded and interpreted information.

For example, an RF circuit 965 receives a HARQ-ACK from the UE 900, ortransmits, to the UE 900, an A-DAI field, a T-DAI field, a DL T-DAIfield, a UL T-DAI field, a downlink grant, an uplink grant, a PDSCH, aPDCCH, a higher layer signaling, or the like.

Particularly, the processor 960 may generate an A-DAI field, a T-DAIfield, a DL T-DAI field, a UL T-DAI field, a downlink grant, an uplinkgrant, a PDSCH, a PDCCH, or a higher layer signaling to be transmittedthrough the RF circuit 965.

What is claimed is:
 1. A method of performing hybrid automatic repeatrequest (HARQ) by a user equipment (UE) in a wireless communicationsystem that supports carrier aggregation (CA), the method comprising:receiving, from an evolved nodeB (eNB), a downlink grant on a firstPhysical Downlink Control Channel (PDCCH), the downlink grant includingan accumulated downlink assignment indicator (A-DAI) field and a totalDAI (T-DAI) field, the A-DAI field indicating a sum of the number ofPDCCHs indicating semi persistent scheduling (SPS) release and thenumber of Physical Downlink Shared Channels (PDSCHs) accumulated up to acurrent subframe within a bundling window associated with HARQ-ACKreporting of the UE based on at least one serving cell, and the T-DAIfield indicating a sum of the number of PDCCHs indicating SPS releaseand the number of all PDSCHs scheduled in association with HARQ-ACKreporting of the UE; receiving a first PDSCH indicated by the firstPDCCH, the first PDSCH being transmitted from the eNB; receiving, fromthe eNB, an uplink grant on a second PDCCH, the uplink grant indicatinga transmission of a Physical Uplink Shared Channel (PUSCH); determininga size of a HARQ-ACK codebook to which a HARQ-ACK with respect to thefirst PDSCH is to be mapped, based on the A-DAI and the T-DAI; andtransmitting, to the eNB, the HARQ-ACK with respect to the first PDSCHon the PUSCH.
 2. The method of claim 1, wherein the T-DAI field is 2bits or 3 bits.
 3. The method of claim 1, wherein the all scheduledPDSCHs and the PDCCHs indicating SPS release are counted throughout allsubframes within the bundling window.
 4. The method of claim 1, whereinthe all scheduled PDSCHs and the PDCCHs indicating SPS are counted up tothe current subframe within the bundling window.
 5. The method of claim1, wherein, when a serving cell through which the first PDSCH isreceived is set to a MIMO transmission mode, the size of the HARQ-ACKcodebook is determined by assuming that the HARQ-ACK corresponding tothe first PDSCH is fixed to one of 1 bit and 2 bits.
 6. A user equipment(UE) to perform hybrid automatic repeat request (HARQ) in a wirelesscommunication system that supports carrier aggregation (CA), the UEcomprising: an RF circuit that receives, from an evolved node B (eNB), adownlink grant on a first Physical Downlink Control Channel (PDCCH),receives a first PDSCH indicated by the first PDCCH, the first PDSCHbeing transmitted from the eNB, and receives, from the eNB, an uplinkgrant on a second PDCCH, the uplink grant indicating a transmission of aPhysical Uplink Shared Channel (PUSCH), wherein the downlink grantincludes an accumulated downlink assignment indicator (A-DAI) field anda total DAI (T-DAI) field, the A-DAI field indicates a sum of the numberof PDCCHs indicating semi persistent scheduling (SPS) release and thenumber of Physical Downlink Shared Channels (PDSCHs) accumulated up to acurrent subframe within a bundling window associated with HARQ-ACKreporting of the UE based on at least one serving cell, and the T-DAIfield indicates a sum of the number of PDCCHs indicating SPS release andthe number of all PDSCHs scheduled in association with HARQ-ACKreporting of the UE; and a processor that determines a size of aHARQ-ACK codebook to which a HARQ-ACK with respect to the first PDSCH isto be mapped, based on the A-DAI and the T-DAI, and generates a HARQ-ACKwith respect to the first PDSCH, wherein the RF circuit transmits, tothe eNB, the HARQ-ACK with respect to the first PDSCH on the PUSCH. 7.The UE of claim 6, wherein the T-DAI field is 2 bits or 3 bits.
 8. TheUE of claim 6, wherein the all scheduled PDSCHs and the PDCCHsindicating SPS release are counted throughout all subframes within thebundling window.
 9. The UE of claim 6, wherein the all scheduled PDSCHsand the PDCCHs indicating SPS release are counted up to the currentsubframe within the bundling window.
 10. The UE of claim 6, wherein whena serving cell through which the first PDSCH is received is set to aMIMO transmission mode, the size of the HARQ-ACK codebook is determinedby assuming that the HARQ-ACK corresponding to the first PDSCH is fixedto one of 1 bit and 2 bits.